Systems inhibited against corrosion and/or scale deposition

ABSTRACT

Aqueous or partly aqueous systems are treated against the corrosion of metals, especially ferrous metals, in contact therewith, and/or against scale deposition therefrom, by adding to these systems from 0.1 to 50 000 ppm of 2-hydroxyphosphonoacetic acid having the formula I ##STR1## or a water-soluble salt thereof.

This is a divisional of application Ser. No. 838,890, filed on Mar. 11,1986, now U.S. Pat. No. 4,689,200.

The present invention relates to aqueous or partly aqueous systems,especially to aqueous systems inhibited against corrosion of metals incontact therewith, and/or inhibited against scale deposition therefrom.

In German Offenlegungsschrift No. 2310450, there are described compoundsof formula: ##STR2## wherein R is an alkyl residue having 1 to 4 carbonatoms and X is hydrogen or a hydroxyl group. These compounds and theirwater-soluble salts are said to be useful as complexing agents forpolyvalent metal ions. The compounds are also said to be suitable foruse as corrosion--or scale--inhibitors for cooling water.

In German Offenlegungsschrift No. 2310450, earlier prior art isdiscussed, and distinguished over, in the following terms. German PatentSpecification No. 1045373 is cited and is said to disclose the use ofmethylene diphosphonic acid as a good complexing agent for calcium.

It is stated that, if one phosphonic acid group is replaced by acarboxylic acid group, then undesirable eutrophic (biological nutrient)properties are reduced, but the complexing properties of the resultingphosphonoacetic acid are also substantially reduced. In order to combinegood complexing properties with reduced eutrophic properties,Offenlegungsschrift No. 2310450 teaches that one of the protons of themethylene group of the phosphonoacetic acid must be replaced by a C₁₋₄-alkyl group; the second proton may optionally be replaced by a hydroxylgroup.

In clear contradistinction to this prior teaching, we have now found,surprisingly, that much improved metal corrosion inhibition and/or scaledeposition inhibition, is attained in aqueous systems by theincorporation of 2-hydroxyphosphonoacetic acid as opposed to the use of2-hydroxy-2-phosphonopropionic acid. Moreover, 2-hydroxyphosphonoaceticacid exhibits excellent corrosion inhibition in systems which are onlypartly aqueous e.g. aqueous machining fluids, antifreeze fluids,water/glycol hydraulic fluids and aqueous surface coatings such aswater-based emulsion paints and aqueous powder coatings for metals.

The present invention provides an aqueous or partly aqueous systeminhibited against corrosion of metals, especially ferrous metals, incontact therewith, and/or inhibited against scale deposition therefrom,comprising adding to this system from 0.1 to 50.000 ppm of2-hydroxyphosphonoacetic acid having the formula I ##STR3## or awater-soluble salt thereof.

2-Hydroxyphosphonoacetic acid is a known compound having been describedin U.S. Pat. No. 3,032,500 and, more recently in European PatentApplication No. 0050792. It can be prepared by known methods e.g. byreacting orthophosphorous acid, a salt or a solution thereof, orphosphorus trichloride, with glyoxylic acid, a salt or a solutionthereof.

2-Hydroxyphosphonoacetic acid may be used as the free acid or as awater-soluble salt or partial salt of e.g. an alkali metal, an alkalineearth metal, ammonia or an alkylamine (optionally substituted with oneto six hydroxyl groups) and containing 1 to 20, preferably 1 to 12carbon atoms.

Examples of suitable salts are those of:

Lithium, sodium, potassium, calcium, strontium, magnesium, ammonia,methylamine, ethylamine, n-propyl-amine, trimethylamine, triethylamine,n-butylamine, n-hexylmine, octylamine, ethanolamine, diethanolamine,triethanolamine or morpholine.

0.1 to 50,000 ppm of 2-hydroxyphosphonoacetic acid is added to aqueoussystems in order to inhibit metal corrosion and/or deposition of scalefrom the system.

In practice, the amount of 2-hydroxyphosphonoacetic acid which is addedto the aqueous system to be treated, will vary depending upon thefunction which 2-hydroxyphosphonoacetic acid is required to perform. Forcorrosion-inhibiting protective treatments, optionally in combinationwith scale inhibiting treatments, the amount of 2-hydroxyphosphonoaceticacid added to the aqueous system is conveniently within the range offrom 0.1 to 50,000 ppm (or 0.00001 to 5% by weight), preferably from 1to 500 ppm (or 0.001 to 0.05% by weight), based on the aqueous system.For solely anti-scale purposes, the amount of 2-hydroxyphosphonoaceticacid used is conveniently from 1 to 200 ppm, preferably 1 to 30 ppm,based on the aqueous system.

With respect to aqueous systems which may be treated according to thepresent invention, of particular interest with respect to combinedcorrosion inhibition and anti-scale treatments are cooling watersystems, steam generating systems, set-water evaporators, hydrostaticcookers, gas scrubbing systems and closed circuit heating systems; forcorrosion inhibition treatments alone, aqueous systems of particularinterest include aqueous machining fluid formulations (e.g. for use inboring, milling, reaming, broaching, drawing, turning, cutting, sawing,grinding, and thread-cutting operations or in non-cutting shaping inspinning, drawing or rolling operations), aqueous scouring systems,aqueous glycol antifreeze systems, water/glycol hydraulic fluids; andaqueous based polymer surface-coating systems.

The compound of formula I may be used alone or in conjunction with othercompounds known to be useful in the treatment of aqueous systems.

In the treatment of systems which are completely aqueous, such ascooling water systems, steam-generating systems, sea-water evaporatorsystems, hydrostatic cookers, and closed circuit heating systems,further corrosion inhibitors may be used such as, for example, watersoluble zinc salts; phosphates; polyphosphates; phosphonic acids andtheir salts, for example, acetodiphosphonic acid, nitrilotrismethylenephosphonic acid and methylamino dimethylene phosphonic acid; otherphosphonocarboxylic acids and their salts, for example, those desired inGerman Offenlegungsschrift No. 2632774,2-phosphonobutane-1,2,4-tricarboxylic acid and those disclosed in GB No.1572406; chromates for example, sodium chromate, nirates, for examplesodium nitrate; nitrites e.g. sodium nitrite; benzotriazole,bis-benzotriazole or copper deactivating benzotriazole or tolutriazolederivatives; N-acyl sarcosines; N-acylimino diacetic acids;ethanolamines; fatty amines; and polycarboxylic acids, for example,polymaleic acid and polyacrylic acid, as well as their respective alkalimetal salts, copolymers of maleic anhydride, copolymers of acrylic acid,and substituted derivatives of polymaleic and polyacrylic acids andtheir copolymers.

Moreover, in such completely aqueous systems, the compound of formula Imay be used in conjunction with further dispersing and/or thresholdagents, e.g. polymerised acrylic acid (or its salts),phosphinopolycarboxylic acids (as described and claimed in British Pat.No. 1458235), hydrolysed polyacrylonitrile, polymerised methacrylic acidand its salts, polyacrylamide and copolymers thereof from acrylic andmethacrylic acids, lignin sulphonic acid and its salts, tannin,naphthalene sulphonic acid/formaldehyde condensation products, starchand its derivatives, and cellulose. Specific threshold agents, such asfor example, 2-phosphonobutane-1,2,4-tricarboxylic acid,acetodiphosphonic acid, hydrolysed polymaleic anhydride and its salts,alkyl phosphonic acids, 1-aminoalkyl-1,1-diphosphonic acids and theirsalts, and alkali metal polyphosphates, may also be used.

Precipitating agents such as alkali metal orthophosphates, carbonates;oxygen scavengers such as alkali metal sulphites and hydrazines;sequestering agents such as nitrilotriacetic acid and its salts;antifoaming agents such as silicones e.g. polydimethylsiloxanes,distearylsebacamide, distearyl adipamide and related products derivedfrom ethylene oxide and/or propylene oxide condensations, in addition tofatty alcohols, such as capryl alcohols and their ethylene oxidecondensates; and biocides e.g. amines, quaternary ammonium compounds,chlorophenols, sulphur-containing compounds such as sulphones, methylenebis thiocyanates and carbamates, isothiazolones, brominatedpropionamides, triazines, phosphonium compounds, chlorine andchlorine-release agents and organometallic compounds such as tributyltin oxide.

If the system to be treated according to the invention is not completelyaqueous e.g. an aqueous machining fluid formulation, it may be e.g. awater dilutable cutting or grinding fluid.

The aqueous machining fluid formulations of the invention may be e.g.metal working formulations. By "metal working" we mean "reaming,broaching, drawing, spinning, cutting, grinding, boring, milling,turning, sawing, non-cutting shaping or rolling". Examples ofwater-dilutable cutting or grinding fluids into which the corrosioninhibiting compound of Formula I may ge incorporated include:

(a) Aqueous concentrates of one or more corrosion inhibitors, andoptionally one or more anti-wear additives, used at dilutions of 1:50 to1:100, which are usually employed as grinding fluids;

(b) Polyglycols containing biocides, corrosion inhibitors and anti-wearadditives which are used at dilutions of 1:20 to 1:40 for cuttingoperations and 1:60 to 1:80 for grinding;

(c) Semi-synthetic cutting fluids similar to (b) but containing inaddition 10 to 25% oil with sufficient emulsifier to render the waterdiluted product translucent;

(d) An emulsifiable material oil concentrate containing, for example,emulsifiers, corrosion inhibitors, extreme pressure/anti-wear additives,biocides, antifoaming agents, coupling agents etc; they are generallydiluted from 1:10 to 1:50 with water to a white opaque emulsion;

(e) A product similar to (d) containing less oil and more emulsifierwhich on dilution to the range 1:50 to 1:100 gives a translucentemulsion for cutting or grinding operations.

Mixtures of sodium nitride and triethanolamine have been used to inhibitcorrosion in metal working but because of related toxicity problems, duee.g. to the danger of forming N-nitrosamines, and because of legalregulations in some countries relating to effluents, alternatives to theuse of sodium nitrite are being sought.

For those partly-aqueous systems in which the aqueous system componentis an aqueous machining fluid formulation the compound of formula I maybe used singly, or in admixture with other additives e.g. known furthercorrosion inhibitors and/or extreme-pressure additives.

Examples of other corrosion inhibitors which may be used in theseaqueous systems, in addition to the compound of formula I, include thefollowing groups:

(a) Organic acids, their esters or ammonium, amine, alkanolamine andmetal salts, for example, benzoic acid, p-tert-butyl benzoic acid,disodium sebacate, triethanolamine laurate, iso-nonanoic acid,triethanolamine salt of (p-toluene sulphonamido caproic acid), sodium Nlauroyl sarcosinate or nonyl phenoxy acetic acid;

(b) Nitrogen containing materials such as the following types: fattyacid alkanolamides; imidazolines, for example,1-hydroxyethyl-2-oleyl-imidazolines; oxazolines; triazoles, for example,benzotriazoles; triethanolamines; fatty amines; and inorganic salts, forexample, sodium nitrate;

(c) Phosphorus containing materials such as the following types: aminephosphates, phosphonic acids or inorganic salts, for example, sodiumdihydrogen phosphate or zinc phosphate;

(d) Sulphur containing compounds such as the following types: sodium,calcium or barium petroleum sulphonates, or heterocyclics, for example,sodium mercaptobenzothiazole.

Nitrogen containing materials, particularly triethanolamine, arepreferred.

Examples of extreme pressure additives which may be present in thesystems of the present invention include sulphur and/or phosphorusand/or halogen containing materials, for instance, sulphurised spermoil, sulphurised fats, tritolyl phosphate, chlorinated paraffins orethoxylated phosphate esters.

When triethanolamine is present in the aqueous systems treated accordingto the present invention, it is preferably present in an amount suchthat the ratio of compound of formula I to triethanolamine is from 2:1to 1:20.

The partly-aqueous systems treated by the method of the presentinvention may also be aqueous surface-coating compositions e.g. primeremulsion paints and aqueous powder coatings for metallic substrates.

The aqueous surface-coating composition may be e.g. a paint such asstyrene-acrylic copolymer emulsion paint, a resin, latex, or otheraqueous based polymer surface-coating systems.

Sodium nitrite and sodium benzoate have been used to inhibit flashrusting of aqueous based primer paints but because of related toxicityproblems and problems of emulsion stability at the high ionicconcentrations used, industry is moving away from sodium nitrite andsodium benzoate.

In aqueous surface-coating compositions treated according to theinvention the compound of formula I may be used singly, or in admixturewith other additives e.g. known corrosion inhibitors, biocides,emulsifiers and/or pigments.

The further known corrosion inhibitors which may be used are e.g. thoseof classes (a), (b), (c) and (d) hereinbefore defined.

Examples of biocides which may be used in these aqueous systems, inaddition to the compound of formula I, include the following:

Phenols, and alkyl- and halogenated phenols, for examplepentachlorophenol, o-phenyl phenol, o-phenoxyphenol and chlorinatedo-phenoxyphenol, and salicylanilides, diamines, traizines andorganometallic compounds such as organomercury compounds and organotincompounds.

Examples of pigments which may be used in these aqueous systems, inaddition to the compound of Formula I, include titanium dioxide, zincchromate, iron oxide and organic pigments such as the phthalocyanines.

The following Examples further illustrate the present invention. Partsand percentages shown therein are by weight.

The 2-hydroxyphosphonoacetic acid active ingredient used in thefollowing use Examples 2 to 6 was prepared as follows:

EXAMPLE 1

(A) 16.3 parts (0,11 mole) 50% aqueous glyoxylic acid and 8.2 parts (0.1mole) orthophosphorous acid are heated together with stirring at98°-100° for 24 hours to give 24.5 parts of 60% aqueous2-hydroxyphosphonoacetic acid.

(B) 150 parts of 60% aqueous solution of 2-hydroxyphosphonoacetic acidobtained according to Example 1A is evaporated under reduced pressure(20 millibars) to give 104 parts of a viscous brown oil. Then this oilis induced to crystallise. The crude crystalline mass is then trituratedwith acetone to remove impurities. The resulting buff colouredcrystalline 2-hydroxyphosphonoacetic acid is removed by filtration,washed with acetone, and dried.

The crude crystalline 2-hydroxyphosphonoacetic acid so obtained is thenrecrystallised from water to give pure 2-hydroxyphosphonoacetic acid aswhite crystals m.p. 165°-167.5° C.

³¹ P-NMR δ=-14 ppm (relative to external H₃ PO₄);

'H-NMR P--CH δ=4.24 ppm ^(J) P--CH=18 Hz

IR COOH: 1745 cm⁻¹, P=0: 1200 cm⁻¹

EXAMPLE 2

Corrosion inhibitor activity of the active compound of formula I isdemonstrated in the following way by the Aerated Solution Bottle Testand using a standard corrosive water made up as follows:

20 g. CaSO₄.2H₂ O

15 g. MgSO₄.7H₂ O

4.6 g. NaHCO₃

7.7 g CaCl₂.6H₂ O

Distilled water 205 liters

Mild steel coupons, 5 cms.×2.5 cms. are scrubbed with pumice, immersedfor one minute in hydrochloric acid and then rinsed, dried and weighed.

The desired proportion of additive combination is dissolved in 200 ml.of standard corrosive water. Two steel coupons are suspended in thesolution, and the whole is stored in a closed bottle in a thermostat at40° C. During the storage period, air is passed into the solution at 500ml/minute, the passage on the air being screened from the steel coupon;any water losses by evaporation are replaced with distilled water.

After 64 hours, the steel coupons are removed, scrubbed without pumice,immersed for one minute in hydrochloric acid inhibited with 1% by weightof hexamine and then rinsed, dried and reweighed. A certain loss inweight will have occurred. A blank test i.e. immersion of mild steelspecimens in the test water in the absence of any potential corrosioninhibitor, is carried out with each series of tests. The corrosion ratesare calculated in milligrams of weight loss/q. decimeter/day (m.d.d.)but for convenience the results are shown as percentage protection,which is defined as follows: ##EQU1## The results obtained in a seriesof tests using 100 ppm, 90 ppm, 80 ppm, 70 ppm, 60 ppm, 50 ppm and 40ppm respectively, of hydroxyphosphonoacetic acid, as produced in Example1 (A) are set out in Table 1.

                                      TABLE 1                                     __________________________________________________________________________    Mild Steel Corrosion Inhibition of hydroxyphosphonoacetic acid in a           Standard Corrosive Water                                                                     % Corrosion Inhibition                                         Example                                                                            Structure 100 ppm                                                                            90 ppm                                                                            80 ppm                                                                            70 ppm                                                                            60 ppm                                                                            50 ppm                                                                            40 ppm                                __________________________________________________________________________          ##STR4## 100  100 100 100 100 99  97.5                                  __________________________________________________________________________

The results in Table I show the effective mild steel corrosioninhibitory properties of hydroxyphosphonoacetic acid.

EXAMPLE 3

The corrosion resistance of an aqueous cutting fluid composition of theinvention is assessed by the following procedure, which is amodification of the Institute of Petroleum Test 287.

A 1% aqueous solution of the compound under test is prepared containingsufficient triethanolamine (TEA) to bring its pH value to 9.

This solution is further diluted by factors of 2, 4, 8 and 16 and eachof these solutions contacted with cast iron chips according to themethod set forth in the IP 287 Test Procedure. This test is carried outusing de-ionised water and IP 287 hard water.

The visual assessment of the condition of the metal chips after exposureis in accordance with the following guidelines.

    ______________________________________                                        Degree of rusting     Rating                                                  ______________________________________                                        no rusting            0                                                       ≧5 small specks                                                                              T (trace)                                               ______________________________________                                    

The results obtained are set out in Table 2, and show thecorrosion-inhibiting activity of the compounds of formula I in anaqueous fluid composition.

                                      TABLE 2                                     __________________________________________________________________________    Cast Iron Corrosion Inhibition in Aqueous Cutting Fluids                                                IP 287 Test                                                        % TEA for 1%      Rust  Rust                                                  of the Compound                                                                          Dilution*                                                                            (deionised                                                                          (hard                                  Example                                                                            Structure of Example                                                                             pH                                                                              Ratio                                                                             %  water)                                                                              water)                                 __________________________________________________________________________          ##STR5## 12.5     9.0                                                                             1:15 1:30 1:60 1:120                                                              0.5 0.25 0.125 0.062                                                             O O O T                                                                             O O T T                                __________________________________________________________________________     *"Dilution Ratio" is the ratio of triethanolamine + compound to water         "Dilution %" is the percentage concentration of the compound only.       

EXAMPLE 4

The effectiveness of the compound of formula I in inhibiting flashrusting is demonstrated in the following way.

A typical primer styrene-acrylic copolymer emulsion paint is prepared tothe following formulation using a high speed stirrer, all parts being byweight

    ______________________________________                                        Zinc orthophosphate   190      parts                                          Titanium dioxide RCR-2                                                                              58       parts                                          Modocol ® EK-600 (4% in water)                                                                  64       parts                                          (a polyacrylate)                                                              Vinapol ® 1640 (5% in water)                                                                    36       parts                                          (Potassium polymethacrylate-Vinyl                                             Products Ltd.)                                                                Ammonia (0.880)       10       parts                                          Water                 92       parts                                          Vinacryl ® M 175  549      parts                                          (Styrene/acrylic copolymer-Vinyl                                              Products Ltd.)                                                                Acticide ® MPM    1        part                                           (Organo-mercury compound -Thor                                                Chemicals Ltd.)                                                                                     1000     parts                                          ______________________________________                                    

An aqueous mixture of the compound of formula I as obtained in Example1(A) and triethanolamine (TEA) (Compound of formula 1:TEA:WATER, 3:48:2by weight) is incorporated, with stirring into 100 g aliquots of thisprimer to give a concentration of 500, 250 and 100 ppm of the compoundof formula 1. A control, without corrosion inhibitor is included forreference.

Paint samples are applied by brush to duplicate steel panels (15.24cm×10.16 cm (which had been freshly blast-cleaned to Sa 3. One coat isapplied over the face of the panels and, when dry, a second coat is thenapplied over half the panel (brushing out at right angles to thedirection of brushing of the first coat). The painted panels are allowedto dry in a controlled environment (20° C., 60% RH) and a visualassessment of flash rusting is then made.

The flash rusting is evaluated visually and according to the number andnature of the rust specks given a numerical rating on a scale from 0 to5; 0=no flash rusting, 5=severe flash rusting.

The results obtained are set out in Table 3.

                  TABLE 3                                                         ______________________________________                                        Steel Corrosion Inhibition in                                                 styrene-acrylic Copolymer Emulsion Paint                                                          Level of Inhibitor                                                                           Rating                                     Panel   Inhibitor   Incorporation (ppm)                                                                          1st Coat                                   ______________________________________                                        1                       2000         0                                        2                       2000         0                                        3                       500          0/1                                      4           Compound of 500          0/1                                      5           formula I   250          0/1                                      6                       250          0/1                                      7                       100          2/3                                      8                       100          2/3                                       9                                    4                                                   No inhibitor                                                      10                                   4                                        ______________________________________                                    

The results in Table 3 show the superior corrosion inhibition ofemulsion paint containing 2-hydroxyphosphonoacetic acid, relative to acontrol paint.

EXAMPLES 5 AND 6

Threshold Test for Calcium Carbonate

The following solutions (a), (b) and (c) are prepared:

(a) Calcium nitrate solution

1.470 grams of calcium nitrate tetrahydrate are dissolved in deionisedwater and the solution is made up to 1 liter;

(b) Sodium carbonate solution

0.646 gram of sodium carbonate is dissolved in de-ionised water and thesolution is made up to 1 liter.

(c) Solution of 2-hydroxy-phosphonoacetic acid

2-hydroxy-phosphonoacetic acid as obtained in either Example 1 (A) or 1(B) is dissolved in water to give a solution containing 1000 ppm ofactive ingredient.

50 mls. of the calcium nitrate solution are placed in a 120 g. glassbottle fitted with a screw cap. To this solution is added that volume ofsolution (c) required to produce a concentration of2-hydroxy-phosphonoacetic acid of 5 ppm, 7.5 ppm or 10 ppm,respectively, in the final volume (100 ml) of test solution (e.g. 1.0 mlof 0.1% of solution (c) produce a concentration of 10 ppm of2-hydroxy-phosphonoacetic acid in the test solution). 50 ml of solution(b) are added and the mixture is shaken. The test solution is stored ina constant temperature bath, maintained at 25° C., for 24 hours.

25 mls. of the test solution are withdrawn, a crystal of Patton andReader's Reagent[2-hydroxy-1-(2'-hydroxy-4'-sulpho-1'-naphthylazo)-3-naphthoic acid] isadded, followed by two pellets of sodium hydroxide. The resultingsolution is titrated with a standard 0.01M solution of ethylenediaminetetra-acetic acid di-sodium salt.

The results, as set out in the following Table 4, are expressed as %inhibition of precipitation of calcium carbonate relative to a blanktitre (i.e. one containing no 2-hydroxyphosphonoacetic acid). ##EQU2##7.78 is the maximum possible titration for 100% inhibition.

    ______________________________________                                                       % Inhibition of precipitation at                                              additive level of                                              Example                                                                              Inhibitor Structure                                                                         5 ppm    7.5 ppm 10 ppm                                  ______________________________________                                                ##STR6##     92.0     93.5    96.5                                    6                                                                                     ##STR7##     89.4     95.2    95.9                                    ______________________________________                                    

EXAMPLE 7

The combined scale and corrosion inhibition properties of the inventionare assessed by the following procedure in evaporative cooling waterrigs.

The standard method of operation of a rig is to concentrate the water tothe desired degree. Once concentrated, the pre-weighed corrosion couponsand heat exchanger are put into the rig and the inhibitor added. Apassivation dose of scale/corrosion inhibitor is added in the feedwaterfor a period of three days, after which the levels of inhibitor areallowed to fall to the maintenance dose level over a period of 2 days.Once the inhibitor dose level is at the desired maintenance level,sufficient scale/corrosion inhibitor is added in the feedwater tomaintain that level for 10 days. After this time, the corrosion ratesare calculated by the weight loss of the metal coupons, and the scalingrate determined by the weight gain of the heat exchanger.

Standard operation parameters for the evaporative cooling water rigs:

System volume 20 liters

Flow rate 15 liters/min

Flow velocity 0.3 meters/second

System temperature 40° C.

ΔT across heat exchanger 2° C.

Half life approx. 30 hours.

Typical analysis of water used.

    ______________________________________                                        pH           8.9                                                              pA(*)        120    ppm        (as CaCO.sub.3)                                TA(*)        470    ppm        (as CaCO.sub.3)                                TH(*)        450    ppm        (as CaCO.sub.3)                                Cl           75     ppm        (as Cl.sup.-)                                                                          Mild                                                                          steel                                 Ex-               Active        Scaling corrosion                             am-  Inhibitor    Dose    Time  rate    rate                                  ple  Structure    (ppm)   (days)                                                                              grams/day                                                                             MDD                                   ______________________________________                                        --   Control      --      --    2.85    32.5                                        ##STR8##    75 15                                                                                  ##STR9##                                                                            0.15     6.1                                 ______________________________________                                         *pA denotes "phenol alkalinity" TA denotes "total alkalinity" and TH          denotes "total hardness"-                                                

What is claimed is:
 1. A method of inhibiting scale formation on andcorrosion of metal surfaces, comprising contacting said surfaces with ascale forming or corrosive medium which contains 1 to about 5 ppm of2-hydroxyphosphonoacetic acid, or a salt thereof which is soluble in themedium.
 2. The method according to claim 1, wherein the medium containsmetal ions selected from the group consisting of calcium magnesium ormixtures thereof, and the medium and metal surfaces are those containedin a cooling system, a steam generating system, a saline evaporator, ahydrostatic cooker, a gas scrubbing system or a closed circuit heatingsystem.
 3. The method according to claim 1, wherein the2-hydroxyphosphonoacetic acid or salt thereof is present in conjunctionwith at least one member selected from the group consisting of adispersing or threshold agent, a precipitating agent, an oxygenscavenger, a sequestering agent, an antifoaming agent or a biocide. 4.The method according to claim 1 wherein the medium further comprisestriethanolamine.
 5. The method according to claim 4 whereintriethanolamine is present in an amount such that the weight ratio of2-hydroxyphosphonoacetic acid to triethanolamine is from 2:1 to 1:20. 6.The method according to claim 1, wherein the 2-hydroxyphosphonoaceticacid or salt thereof is present in conjunction with a differentcorrosion inhibitor.